<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>你说得对</title>
    <link rel="stylesheet" href="css/boxDistance.css">
</head>
<body>
    <div class="box1">
        你好你好
    </div>
    <h1>外边距折叠了</h1>
    <div class="box2">
        你好你好
        你好
    </div>
    <div class="box3">
        你好
    </div>
    <h1>防止塌陷</h1>
    <div class="box4">
        <div class="box5">
            你好
        </div>
    </div>
</body>
</html>